The purpose of the proposed research is to further comprehend the impact of environmental lighting on the physiological and behavioral components of reproductive rhythms. This research will forcus upon the causes of reproductive acyclicity and anovulation in two different rodent models. A first series of studies will investigate the hormonal regulation of anestrus in the hamster. In this regard we will examine steroid changes in hamsters exposed to short-day photoperiods, the normalcy of feedback relationships in this animal, and the interaction of daylength with steroid feedback. Of interest, too, is the alteration and the interdependence of various rhythmic behaviors as the animal becomes anovulatory: activity, sexual behavior and aggression. Finally, we will attempt to investigate the role of the circadian system in seasonal reproductive processes in the female hamster. A second thrust of the research project will focus on the etiology of the anovulation induced by exposure to constant light in the female rat. We will assess the degree to which thresholds to the negative feedback of steroids on gonadotropins and thresholds to the facilitatory effects of steroids on sexual behavior are altered in this anovulatory state. The level of illumination may be a key factor in suppression of the surge of LH; we will induce daily surges with Silastic capsules of estradiol and implant jugular cannulae to do serial sampling to monitor differential suppression of the surges by light intensity. Finally, we will continue our investigations of the adrenal facilitation of the gonadotropin surge in LL animals.